1. FIELD OF THE INVENTION
The present invention relates to a packaged solar cell apparatus useful as a power supply for a vehicle such as an automobile or other mobile objects, more particularly, to an improvement of a packaged solar cell apparatus which converts sunlight energy into electrical energy and utilizes the electrical energy as a power supply for feeding an instrumentation system or a regulating system mounted on the vehicle, thereby lightening a burden on the vehicle-mounted battery as far as possible.
2. DESCRIPTION OF THE PRIOR ART
As a conventional apparatus in this field, an automobile ventilation system using a solar cell is known as disclosed by Japanese Patent Application Laid-Open No. 140,731/78. The disclosed ventilation system is intended to prevent an increase of the temperature in a passenger copartment of an automobile by ventilating the passenger compartment, while the automobile is parked, by driving a fan with electrical output energy generated by a solar cell mounted on the body of the automobile. The ventilation system has an advantage such that the electrical output energy, that is, an amount of generated electric power increases as the radiation intensity of sunlight increases, thereby causing an increase in a rotational speed of the fan and hence in a ventilation air flow, so that ventilation capacity can be controlled automatically in response to insolation intensity, without requiring any special control device to make the rotational speed of the fan adapted to a change of weather. However, because of the relation between a load current versus a voltage characteristic of the fan and an output current versus an output voltage characteristic of the solar cell, it is impossible to use the solar cell always in an optimum condition regardless of insolation intensity.
This relation will be explained with reference to FIG. 4. When insolation is intense, two sets of solar cells connected in series exhibit a V-I characteristic as shown by (B), and hence an output power thereof has an output characteristic as indicated by (B'). If a fan of a V-I characteristic shown by (A) is used as an example of a load on the solar cells, the operating point becomes the intersection a of the curves (A) and (B), and the maximum output point is shown by the point a'. However, when insolation intensity decreases, the serially connected solar cells exhibit output characteristics shown by the curves (C) and (C'), and the operating point becomes the intersection b of the curves (A) and (C) and the output power is shown by the point b' on the curve (C') which deviates from the maximum output point on the curve (C'). As described above, even if the solar cells have been adapted to operate at their optimum operating point when insolation intensity is high, the operating point thereof deviates from the optimum operating point when insolation intensity becomes low. Conversely, even if the solar cells have been adapted to operate at their optimum operating point when insolation intensity is low, the operating point thereof deviates from the optimum operating point when insolation intensity becomes high. Thus, it is difficult to make the fan operate always at an optimum operating point of the serially connected solar cells in either case.